The present invention relates generally to vehicular suspension systems. More particularly, the invention relates to a vehicle damper assembly and method for modulating fluid flow.
Linear suspension dampers, such as shock absorbers and McPherson struts, may include a rod and piston moving within a fluid-filled housing. Suspension movements transmitted to the rod and piston may be dampened as the damper compresses and extends. Desirable damper performance usually requires that significantly greater dampening force is generated during an extension stroke as compared to compression. The use of a magnetorheological (MR) fluid may be utilized to provide such dynamic dampening forces.
MR fluids are generally suspensions of magnetic particles such as iron or iron alloys in a fluid medium. The flow characteristics of these fluids can change by several orders of magnitude within milliseconds when subjected to a suitable magnetic field due to suspension of the particles. The ferromagnetic particles remain suspended under the influence of magnetic fields and applied forces. Such MR fluids are well known and have been found to have desirable electromagnetomechanical interactive properties for controlling dissipative forces along the damper""s axis.
A linear acting MR damper piston may include a coil assembly, a core, and an annular piston ring positioned around the pole pieces to form an annular flow passage or gap. When the piston is displaced, MR fluid is forced through the gap from one area of the damper housing to another. When the coil is energized, a magnetic field permeates the gap and excites a transformation of the MR fluid to a state that exhibits increased damping force (i.e., the MR fluid viscosity is increased). Thus, the dampening force may be controlled by adjusting the current run through the coil assembly. In addition, this mechanism may be used to provide greater dampening force during the damper extension stroke.
Using MR state transformation to generate greater dampening force during extension may have disadvantages. For example, the ability of MR damper to manage finely-tuned dampening or other events may be diminished as a good deal of controllable dampening capacity is utilized to generate extension stroke dampening force. It would be desirable if the MR dampening capacity could be preserved to handle finely-tuned dampening and/or other events requiring additional dampening force. For dampers lacking MR fluid altogether, such dampers may not possess means for generating greater dampening force during the extension stroke. Accordingly, it would be desirable to provide a strategy for modulating the fluid flow through a damper piston thereby regulating the dampening force generated during extension and compression strokes.
Therefore, it would be desirable to provide a vehicle damper assembly and method for modulating fluid flow that overcomes the aforementioned and other disadvantages.
One aspect of the present invention provides a vehicle damper assembly. The assembly includes a housing including a fluid carried therein. A piston is slidably carried in the housing and includes a ring and a core. At least one gap to allow fluid flow is formed between the ring and core. A rod is operably attached to the piston. The ring moves axially with respect to the core to vary the gap size and modulate fluid flow during operation of the assembly. The fluid may be a magnetorheological fluid. The gap may be formed between at least one ring shoulder portion and at least one core shoulder portion. The gap may expand during a compression stroke and/or narrow during an extension stroke. The gap size may be inversely proportional to a dampening force. The piston may include a plurality of projections adapted to provide a limited range of motion relative to the core. At least one spring may be operably attached to the piston and adapted to force the ring against at least one of the projections.
Another aspect of the invention provides a method for modulating fluid flow through the vehicle damper assembly. The method includes axially moving a ring with respect to a core during assembly operation. At least one gap size is varied based on the axial movement, wherein the gap is formed between the ring and core. The gap may expand during a compression stroke and/or narrow during an extension stroke. The gap size may be inversely proportional to a dampening force. A ring range of motion relative to the core may be limited. The ring may be forced against at least one projection.
Another aspect of the invention provides a vehicle damper assembly. The assembly includes means for axially moving a piston ring with respect to a piston core during damper operation. The assembly further includes means for varying at least one gap size based on the axial movement, wherein the gap is formed between the ring and core.